1. Field of the Invention
The present invention relates to an integrated light emitting and receiving device and an optical pick-up for emitting light to a recording medium, receiving reflected light modulated by pits formed on the recording medium, and detecting the focus condition and tracking condition based on the information of the reflected light.
2. Description of the Related Art
Recently, various kinds of recording media including recording media using a change of reflectance, optomagnetic recording media, and the like have been developed and proposed. Various kinds of optical disc players have been proposed and standardized.
In compact disc (CD), compact disc-read only memory (CD-ROM), and other so-called phase type optical disc players, the standards call for the depth of the pits formed in the optical disc to be about 1/5 of the wavelength of light.
On the other hand, in digital versatile disc (DVD), digital versatile disc-read only memory (DVD-ROM), and other more recent optical disc players, the standards call for the depth of the pits to be about 1/4 of the wavelength of light.
In the above optical disc players, it is necessary to control the tracking servo system so as to make a laser spot follow the recording track of the optical disc and to control the focus servo system so as to keep the laser spot focused on the optical disc.
The tracking error signal and focus error signal for the tracking servo system are detected by for example an optical pick-up.
For example, as shown in FIG. 1, an optical picks-up is comprising of an object lens 2 arranged facing an optical disc 1 and a so-called laser coupler 3 hybridized for reducing the size and cost.
The laser coupler 3 has the structure illustrated in FIG. 2 and FIG. 3. In the laser coupler 3 shown in FIG. 2 and FIG. 3, a prism 8 and a photodiode 11 are mounted on a semiconductor integrated circuit substrate 4 on which two photodetector 5 and 6 are formed.
In the photodiode 11, a photodetector 12 for monitoring the laser output is formed. A laser diode 10 is mounted on the photo diode 11.
The laser diode 10 outputs a laser beam to the beam splitting face 8a of the prism 8 and outputs a laser beam for auto power control (APC) to the laser which automatically controls the output of the laser diode 10. The laser beam is received by the photodetector 12. The laser beam output to the beam splitting face 8a of the prism 8 is reflected on the beam splitting face 8 and is focused on the signal face of the optical disc 1 through the object lens 2.
The light is influenced by the pits of the optical disc 1 and is reflected to enter into the beam splitting face 8a through the same path.
The reflected light entering into the beam splitting face 8a is focused on the photodetector 5 and the reflected light on the photodetector 5 is reflected on the reflection face 8b to enter the photodetector 6.
When obtaining a tracking error signal by the so-called push-pull method and obtaining a focus error signal by the so-called differential spot size method in a CD, CD-ROM, or other optical disc player, it is possible to adopt the configuration for example shown in FIG. 4.
In FIG. 4 the photodetectors 5 and 6 are each split into four light receiving regions a to d, i to e. The spot S of the reflected light strikes all of the receiving light receiving regions.
Note that the push-pull method features a very simple configuration and since basically a one-spot optical system is sufficient does not need grating such as in the so-called three-beam method.
If the tracking error signal is TE, the focus error signal is FE, and the amounts of the received light of the receiving light regions a to d and i to l are Ma to Md and Mi to Ml, the tracking error signal TE and the focus error signal FE can be calculated by the following equations (1) and (2): EQU FE=[(Ma+Md)-(Mb+Mc)]-[(Mi+Ml)-(Mj+Mk)] (1) EQU TE=[(Ma+Mb)-(Mc+Md)]+[(Mk+Ml)-(Mi+Mj)] (2)
An information signal RF recorded on the optical disc 1 can be calculated by the following equation (3): EQU RF=Ma+Mb+Mc+Mc+Md+Mi+Mj+Mk+Ml (3)
On the other hand, in DVD, DVD-ROM, or other the optical disc player, as mentioned above, the depth of the pits of the disc is about 1/4 of the wavelength .lambda. of the laser beam.
Therefore, if obtaining the tracking error signal TE by the above push-pull method, the component [(Ma+Mb)-(Mc+Md)]+[(Mk+Ml)-(Mi+Mj)] of the push-pull signal becomes so small that the tracking error signal cannot be obtained.